Though most retailers include sales made on tablets—through web sites and tablet apps—in their mobile commerce revenue totals, Forrester Research excludes tablets. Research firm eMarketer Inc., which includes tablets in its mobile commerce figures, says mobile sales hit $24.66 billion in 2012, accounting for 11% of total e-commerce sales. Forrester estimates $266.67 billion in total e-commerce sales in 2012, up 15% from $232 billion in 2011. EMarketer estimates $224.2 billion in total e-commerce sales in 2012, up 15% from $194.7 billion in 2011.

While the total number of U.S. smartphone users continues to grow rapidly, only a minority of those consumers have ever made purchases via their mobile phone, Forrester Research says. Forrester estimates that there were 132 million U.S. mobile Internet users in 2012. About 25% of those mobile Internet users made purchases via their phones in the past year, Forrester says.

“While we expect the m-commerce penetration rate to double by 2017, m-commerce in the U.S. is still a tiny portion of e-commerce—and, consequently, a minuscule share of overall retail,” writes Sucharita Mulpuru, vice president and principal analyst, in the report titled “U.S. Mobile Retail Forecast, 2012 to 2017.” “In fact, we estimate that only 3% of all e-commerce transactions, including daily deals but excluding travel, were completed on mobile phones in 2012.”

Mulpuru says the numbers for smartphone sales remain low for a variety of reasons. First, it’s difficult to check out and pay on smartphones, she writes.

“A small minority of companies have publicly stated or implied that a significant volume of their business is generated from mobile devices: These include firms like Amazon.com, eBay and Fandango, as well as a number of daily deal sites, such as Gilt Groupe and Groupon,” Mulpuru writes. “In fact, we estimate that about a third of all U.S. m-commerce retail revenues are generated by sites that can be classified as vehicles for daily deals. The feature common to all these sites? Easy checkout functionality that often preserves shoppers’ shipping and payment information.”

Most retailers have cumbersome checkouts that often require hundreds of keystrokes; only a few have implemented tools like PayPal Express that can facilitate the smartphone checkout experience, she adds. The average mobile site’s conversion rate is 1% versus 2% to 3% for the same site on a PC, Forrester Research says.

Second, most multichannel retailers continue to generate most of their business from stores and consequently focus on stores, Mulpuru writes.

“Mobile gives stores a welcome opportunity to use the web to support their primary channel,” she writes. “As a result, more retailers are focusing on the elements of the mobile site experience that can help in-store shoppers and even store associates rather than on generating transactions via those devices. For instance, they have prioritized product information, ratings and reviews rather than checkout and payment options.”

And third, most mobile transactions are limited to a few categories, Mulpuru writes. Consumers report researching a number of different categories on mobile devices; however, the vast majority of m-commerce retail transactions that are not daily deal purchases are in the media and consumer electronics categories, Forrester Research says.

“75% of non-daily deal retail mobile transactions are in those two categories alone,” Mulpuru writes. “This is indicative of both the ease of purchasing in these categories and the level of showrooming that exists in the consumer electronics category in particular.”

Showrooming is the practice by some consumers of checking out products in stores then using their smartphones to compare prices with competitors, buying a product later online or then and there via mobile.

To maximize their investments in smartphone-based mobile commerce, retailers should focus on easy transactions and responsive web design, Mulpuru writes.

“Make sure that you have a fast checkout solution,” she writes. “PayPal Express is a good option because it already has a large base of Internet buyers. Checkout by Amazon and Google Checkout are other obvious solutions, yet they have significantly smaller bases. Remember, the fewer the keystrokes during the mobile checkout process, the higher the conversion rate.”

And retailers should consider building a responsive web design e-commerce site, Mulpuru advises. Responsive design tailors web site content to fit the size and shape of the screen of the device requesting a web page. That device could be a PC, a tablet, a smartphone or a TV. A single responsive web site can adapt to a screen of any size.

“The challenge with executing this approach, particularly for companies that are more than a decade old, is that you must redesign your core web pages to accommodate this option,” Mulpuru writes. “As a result of the complexity, a number of retailers have created one-off solutions for, say, the iPhone or even the BlackBerry, but executives recognize that this is unsustainable over time. Budget now for a responsive design-focused site redesign, as this often involves a large project with technical complexities and a number of stakeholders.”